1. Skin as an organizing model
Original Simplified View
What is it? (Anatomy)
What does it do? (Physiology)
What is it made of? (Histology)
Where does it come from?
(Embryology)
Frolich, Human Anatomy, Skin

2. Skin as an organizing model
What is it? (Anatomy)
What does it do? (Physiology)
What is it made of? (Histology)
Where does it come from?
(Embryology)
[brainstorm—what questions remain?]
Frolich, Human Anatomy, Skin

3. Skin revisited: Filling in the Blanks
Anatomy—dermatomes and spinal nerves
Histology
epidermal cells and layers
dermal layers
other structures
Physiology
details of skin protection function
Pathology of skin
skin cancers
burns
Frolich, Human Anatomy, Skin

4. Frolich, Human Anatomy, Skin
Original Simplified View
What is it (anatomy)?
Outer covering of body
Keratinized
Hair—head, pubic regions
Nails—fingers, toes
Divided into segments called dermatomes (“Zebra-man”)
CE (clinical example): Shingles
Frolich, Human Anatomy, Skin

5. Dermatomes and spinal nerves
Dermatomes—more details
Dermatomes and spinal nerves
Frolich, Human Anatomy, Skin

6. Dermatomes and segmentation in basic body plan
Dermatomes—more details
Dermatomes and segmentation in basic body plan
Frolich, Human Anatomy, Skin

7. Hair and nails—modified structures of epidermis
Epidermis anatomy—more details
Nails
Scale-like epidermal structure
Cells bind together and have “hard” keratin
Grows out from root of nail
Hair
Each shaft has three layers of keratinzed cells filled with “hard” keratin
Flat, ribbon-like shaft produces kinky hair; oval shaft makes wavy hair; round shaft makes coarse hair
Hair color due to amount of melanins of different colors made my melanocytes at base of hair follicle; red hair also has iron-containing pigment; gray/white hair due to decreased melanin production
Hair follicle
Fold of epidermal surface into dermis
Hair grows from here
Has nerve plexus to give touch/tickle sensation
Connective tissue sheath derived from dermis
Hair length due to relationship between active and inactive phases of follicle (e.g., eyebrow follicles active only three to four months; head follicles can be continuosly active for years)
Frolich, Human Anatomy, Skin

8. Nails—scale-like epidermis
Epidermis anatomy—more details
Nails—scale-like epidermis
Frolich, Human Anatomy, Skin

9. Hairs and hair follicles
Epidermis anatomy—more details
Epidermis—more detail
Hairs and hair follicles
Frolich, Human Anatomy, Skin

10. What is it made of? (histology—study of tissues)
Original Simplified View
Layers of skin are two fundamental types of tissue organization
Epidermis = epithelium
Dermis = connective tissue
Frolich, Human Anatomy, Skin

11. Frolich, Human Anatomy, Skin
Epidermis histology—more details
Layers of epidermis
Stratum basale/germinativum (“basal or “forming” layer)
One layer thick mitotic cells
10-25% melanocytes with processes into next layer
Merkel cells with sensory neurons
Stratum spinosum (“prickly” layer)
Cells appear spiny due to numerous desmosomes
Many Langerhans cells
Stratum granulosum (“grainy” layer
Cells flatten
Organelles/nuclei begin to disintegrate
Keratin precursor granules begin to form
Lamellated granules with water-proof lipid form and will be spewed out between cells
Stratum corneum (“horny” layer)
Cells are dead—too far from underlying capillaries to live
20-30 cells thick up to ¾ of dermal thickness
Keratin, thickened membranes and glycolipids between cells provide “overcoat” for body to protect against water loss and other possible “assaults” on body
Frolich, Human Anatomy, Skin

12. Frolich, Human Anatomy, Skin
Epidermis histology—more details
Cells in epidermis
Keratinocytes—epidermal cells that make keratin
Merkel cells—associated with touch sensory neurons
Langerhans cells—macrophages (from dermis) migrate in to form spider-like immune barrier
Melanocytes (at border with dermis) make pigment to give skin color
Frolich, Human Anatomy, Skin

13. Epidermis—a stratified epithelium
Epidermis histology—more details
Epidermis—a stratified epithelium
Frolich, Human Anatomy, Skin

14. Frolich, Human Anatomy, Skin
Original Simplified View
Dermis—simple view
Frolich, Human Anatomy, Skin

15. Frolich, Human Anatomy, Skin
Dermal layers
Dermis histology—more details
Papillary layer (layer with “nipples” or tiny projections)
Thin superficial layer of areolar connective tissue
Papillae house capillary loops, nerve endings, sweat glands
In hands and feet papillae on dermal ridges forming fingerprint patterns
Reticular layer
80% of thickness
Dense irregular collagen fibers, mostly parallel to skin surface
Predominant direction of fibers forms cleavage or tension lines in skin (important for incisions)
Flexure lines in skin at joints where reticular layer is bound to underlying connective tissues to provide “give” when joint flexes
Frolich, Human Anatomy, Skin

16. Glands and keratinized appendages: Is it dermis…or epidermis?
Epidermis/Dermis histology—more details
Glands and keratinized appendages: Is it dermis…or epidermis?
Sebaceous glands
Clumps of epithelial tissue distributed within dermis
Secrete “sebum”—oily, fat-based substance that is also anti-bacterial
Located all over body
Sweat glands
Microscopic clumps of epithelial tissue distributed within dermis, duct extends out through dermis to pore (not “pores” of face complexion which are hair follicles)
More than 2.5 million glands per person
Eccrine sweat glands, concentrated on hands and soles of feet and forehead, secrete sweat to cool body, also “cold sweat” of fear, emotion.
Apocrine glands, concentrated in armpits and groin, analogous with sexual scent glands of other animals, odor comes from bacteria that concentrate here.
Ceruminous glands: modified sweat glands in ear canal produce ear wax
Mammary glands: modified sweat glands in female breast produce mother’s milk
Frolich, Human Anatomy, Skin

17. Frolich, Human Anatomy, Skin
Epidermis/Dermis histology—more details
Skin Glands
Frolich, Human Anatomy, Skin

18. Frolich, Human Anatomy, Skin
Original Simplified View
What does it do?
PROTECTION
Air = desiccation
Water = bloating/”pruning”
Sun/u-v = burns
Cold/heat = frostbite/heat stroke/thermoregulation
STRUCTURAL
Integrity of body
Muscle attachment
Frolich, Human Anatomy, Skin

19. Frolich, Human Anatomy, Skin
Physiology—more details
What does it do?
PROTECTION
Chemical barriers—”acid mantle” from low “pH of skin secretions retards bacterial growth
Water-proofing from lipid secretions of epidermis
Melanin from melanocytes and DNA in all skin cells prevents burning from sun
Immune cells in dermis and epidermis fight infection and present antigens to other immune cells
Evaporation of sweat cools body
Closing of dermal capillaries prevents heat loss
Supplement liver in “disarming” cancer-causing chemicals that penetrate epidermis
SENSATION—nerve endings
METABOLIC FUNCTION—vitamin D synthesis
Frolich, Human Anatomy, Skin

20. Frolich, Human Anatomy, Skin
Pathology of skin
Physiology—more details
Skin cancer (what are the cells involved?)
Basal cell carcinoma (a)
Common and benign, 30% of white people get, slow-growing and easily incised surgically
Squamous cell carcinoma (b)
Less common, faster-growing but still easily removed surgically
Melanoma (c)
Highly metastatic (spreads rapidly)
Related to U-V exposure
Early detection key—can start in retina (importance of ophthalmologic exams)
Frolich, Human Anatomy, Skin

21. Frolich, Human Anatomy, Skin
Physiology—more details
Frolich, Human Anatomy, Skin

22. Frolich, Human Anatomy, Skin
Physiology—more details
Pathology of skin
Burns
Rule of nines
Degree of burns
Synthetic skin from silicon epidermis and spongy dermis made of collagen fibers and ground cartilage
Frolich, Human Anatomy, Skin

23. Interrelationship with other systems
Physiology—more details
Interrelationship with other systems
Systems are not isolated, but just one way of analyzing how body works
Skin is tightly linked to other systems of body
Skeletal: Skin forms “exoskeleton”—stiff attachment point for muscles; also synthesizes Vitamin D necessary for calcium deposit process
Muscular: Many muscles attach on the skin; muscles lose heat through skin
Nervous: Sensory cells (Merkel cells) transmit touch sensation to neurons; blood vessel, sweat, arrector pili muscles controlled by nervous system
Cardiovascular: Skin as blood reservoir, heat exchange organ
Immune: Very important role of skin as “first barrier” with Langerhans cells and macrophages as cellular immune response; edema or swelling common in infected skin regions
Reproduction: skin responds to erotic stimuli; mammary glands are highly modified sweat glands in skin; stretching of skin to accomondate fetus during pregnancy
Frolich, Human Anatomy, Skin

24. Frolich, Human Anatomy, Skin
New Topic of Interest
Electronic Skin
Frolich, Human Anatomy, Skin

25. Distribution of skin Color
New Topic of Interest
Distribution of skin Color
Skin color around world
Frolich, Human Anatomy, Skin

26. Frolich, Human Anatomy, Skin
New Topic of Interest
Genetics of skin color
From Genetics Chapter
On-Line Biology Book
Frolich, Human Anatomy, Skin